98 Excel loss of power, intermittent
 

About a year ago, my Excel X3 twin 1.5 DOHC started "playing up". Initially thought dirty injectors, as it was like dirt in a carby in the "old days", sometimes went well, then slowed down and had little power. I tried to book it into the Hyundai dealership in towm, but they refused to take the booking without the VIN no. The car was 700 M away at the time, so I told them not to bother, I'd go elsewhere. So I ran a foaming injector cleaner through it, no change. Replaced the plugs, tested the HT leads, OK. Found one of the ignition coils black inside the plug lead connector, and smelled burnt, thought "Ah ha, found it". Replaced the coil pack with a good second hand unit, no difference. Took it to a general mechanic, who cleaned the throttle body, and replaced the plugs again and replaced the HT leads, AGAINST my instructions, still no better. Pulled the injectors, sent them to a performance shop and had them cleaned and tested, no change. Pulled the fuel pump, checked the inside of the tank, OK. Replaced the air, oil and fuel filters, no change. Made up a fitting on the banjo bolt on the fuel filter to check fuel pressure while driving, OK, in specs, and no difference between going well, and running like a slug. Took it back to the performance shop, can't remember what they did, (SFA), still no better, but I was $170 lighter. I've had the exhaust system checked, in case it was a broken cat blocking the exhaust flow, but was assured it wasn't that. Finally bit the bullet, and took it back to Hyundai dealer, same story about the VIN, so I asked to speak to a manager, who said "no probs, we can take the booking without VIN, the girl shouldn't treat you like that" (tell me something I don't know). They had the car for a day, said they couldn't fault it, it went well for them, all they fouind was a code for the knock sensor in the engine computer. I've long suspected the knock sensor, as I feel that when its running poorly, its not running rough, like a miss, or on 2 or 3 cyls, rather, all cyls are firing, and its still smooth, just gutless and sounds funny. I have to "rev the crap out of it" to get anywhere. So I feel that retarded timing could be causing the fault, which could be caused by a faulty knock sensor, I think. But as Hyundai wanted to charge $250 odd to replace it, with no certainty whatsoever, that this would be the problem, I said "no, I want it properly diagnosed before you start replacing this and that, in the vain hope that you might stumble upon the fault". So I'm still trying to diagnose it myself, and am thinking of buying a scan tool and leaving it on while I'm driving it, so I can cancel the fault (knock sensor) when its going well, and see if that fault only comes basck when it "plays up".

Anyone care to comment, or got any other ideas?

I recommend check the MAF, mass air flow sensor, the PCV they could be faulty. Other wise I feel you are back to the timing.

Thanks JP, I haven't had time to check the MAF yet, most likely won't get a chance till I have some time off around Christmas. What is the PCV? Positive Crankcase Vent maybe? I tried to fit a camera and timing light to it to check the timing while driving, but just not enough room there to get both in place. But thanks for your comments.

I'm rather astounded that after two weeks, I've only had one response to my post. I thought I'd have been swamped with bright ideas (and some not so bright), on a dedicated Hyundai forum,m with such a popular model car.

i had similar issue with my australian 96' excel, i swapped the stock oxygen sensor (never been replaced) out for a bosch 13843, really cheap and sorted problem. have you ever replaced your fuel filter?
Hyundai Mitsubishi Oxygen Sensor (Excel Precis) - Bosch 13843 | FCP Import

Thanks Redline, I will try that. Although I've replaced the Excel with a Diesel I30, I still love the Excel, and will do her up, if I can solve this problem.And yes, I did replace the fuel filter, and tested the fuel pressure.